ci: change default fabric print grey level from 15% to 10%

Change-Id: I07f69dc4a42c1b481cae687eed7187bb8775e09b
diff --git a/ci/pdf-lighten-black b/ci/pdf-lighten-black
index e24b565..390e6ca 100755
--- a/ci/pdf-lighten-black
+++ b/ci/pdf-lighten-black
@@ -2,7 +2,7 @@
 # pdf-lighten-black IN.pdf [OUT.pdf] [GREY]
 #
 # Produce a copy of IN.pdf in which all *vector* pure black is replaced by a
-# dark grey (default 15% = #262626). Intended for printing on fabric, where
+# dark grey (default 10% = #1a1a1a). Intended for printing on fabric, where
 # solid black ink bleeds out, making QR codes hard to scan and text fuzzy.
 #
 # Works on the PDF content streams directly (qpdf QDF round-trip), so text
@@ -10,11 +10,11 @@
 # file works at any print resolution. Colors inside embedded raster images
 # (e.g. screenshots) are not touched.
 #
-# GREY is the target grey level in [0,1) per RGB channel (0.15 = 15% = #262626).
+# GREY is the target grey level in [0,1) per RGB channel (0.10 = 10% = #1a1a1a).
 
 in=$1
 out=${2:-${in%.pdf}_fabric.pdf}
-grey=${3:-0.15}
+grey=${3:-0.10}
 
 k=$(awk -v g="$grey" 'BEGIN { printf "%.4g", 1 - g }')